Why doesn't my light beam render?
There is likely nothing wrong with your setup.
The issue is with the render viewport not being able to display emissive and transparent pixels.
To check this try either

Disabling Film&gt;Transparent

or compositing your image over some color (or black) background,

or simply looking at the RGB image with no alpha on the viewer.
Related: Transparent Image different in viewport than render  - and How do I get the Glare node to output transparent instead of Black background